Due to the explosive growth in mobile broadband traffic and its concomitant strain on limited spectrum resources, the Federal Communications Commission has adopted rules to allow commercial shared use of 150 MHz of spectrum in the 3550-3700 MHz (3.5 GHz) band for licensed and unlicensed use of the 3.5 GHz band for a wide variety of devices.
Citizens Broadband Radio Service (CBRS) is a tiered commercial radio service in 3.5 GHz in the U.S. Channels are allocated within and across tiers. These tiers can include, in order of priority, (1) incumbent licensees; (2) Priority Access (PA) licensees; and (3) General Authorized Access (GAA) operators. Portions of spectrum that are not continuously used by an incumbent licensee can be allocated to the secondary users that is, PA licensees and GAA operators.
A Priority Access License (PAL) is an authorization to use a channel (e.g., an unpaired 10 MHz channel) in the 3.5 GHz range in a geographic service area for a period (e.g., 3 years). The PAL geographic service area may be census tracts, which typically align with the borders of political boundaries such as cities or counties. PAL licensees can aggregate up to four PA channels in any census tract at any given time, and may obtain licenses in any available census tract. PALs may provide interference protection for Tier 1 incumbent licensees and accept interference from them. However, PALs may be entitled to interference protection from GAA operators.
The third tier, GAA, permits access to bandwidth (e.g., 80 MHz) of the 3.5 GHz band that is not assigned to a higher tier (i.e., incumbent licensees or PAL licensees). GAA operators may be licensed “by rule,” meaning that entities that qualify to be FCC licensees may use FCC-authorized telecommunications equipment in the GAA band without having to obtain an individual spectrum license. GAA operators may receive no interference protection from PA licensees or Tier 1 operators, and may accept interference from them.
In order to facilitate the complex CBRS spectrum sharing process, a Spectrum Access System (SAS), which may be a highly automated frequency coordinator, can be used to assign frequencies in the 3.5 GHz CBRS band. The SAS can also authorize and manage use of the CBRS spectrum, protect higher tier operations from interference, and maximize frequency capacity for all CBRS operators.